02 October 2012

Mono Block Ultra-Linear Class-A Push-Pull EL84 Tube Amplifier Project

Recently Bruce has been enjoying his PoddWatt amplifier and the EL84 tube sound that he has revisited the original OddWatt amplifier project, tweaked it and put together an improved EL84 push-pull amplifier. Like the previous EL84 projects the Mini Block amplifiers use a EL84 self-inverting push-pull output stage that is biased into class-A operation. The big difference is that the amplifiers are built as mono blocks.

Mini Block Push-Pull EL84 (6BQ5) Valve Amplifiers

Interior - Mini Block EL84 Push-Pull Amplifiers

The input circuit is a 5751 SRPP. The ouput uses the ultra-linear connection and output power was 5.8 W @ 2% distortion and less than 0.25% at 1 W. The measured frequency response was 10 Hz to 44 kHz within 0.2 dB. Bruce reports that the Mini
Blocks have slightly more output power than the Poddwatts and seem to have more detail
while retaining all the good characteristics of the stereo Poddwatt amps. Full details are available on the Mini Block Ultra-Linear Class-A Push-Pull EL84 (6BQ5) Valve (Tube) Amplifier Project page.